EPSC Abstracts Vol. 13, EPSC-DPS2019-1920-1, 2019 EPSC-DPS Joint Meeting 2019 c Author(s) 2019. CC Attribution 4.0 license.

Outbursts on comet 67P/Churyumov– Gerasimenko

Zhong-Yi Lin (1), Wing-Huen Ip (1), Jean-Baptiste Vincent (2) and the OSIRIS team (1) Institute of Astronomy, NCU, Taiwan ([email protected]) (2), Institute of Planetary Research, DLR, Berlin Germany Abstract the mechanism for this type of activity is still unknown. Fortunately, unlike the snap shots from the The optical, spectrocopic and infrared remote previous flyby observations, the OSIRIS imaging system (OSIRIS) onboard the Rosetta measurements can provide precise information on the spacecraft provided first-hand information on the timing and location of the outbursts via a time series outbursts from comet 67P/Churyumov–Gerasimenko. of high-resolution images. After the first detection in In this paper, we upgrade the investigation on the 2015 March, the OSIRIS wide-angle camera (WAC) physical properties of the outbursts from July 2015 to and narrow-angle camera (NAC) captured another September 2016. The new map of the source regions outburst in mid-July of 2015. Since then, many more from the detected outbursts has been used for the outbursts from the nightside and sunlit regions have comparison to the measurements from the other been detected, with most of their source regions onboard instruments. located in the Southern hemisphere of comet 67P. The detected outburst events show a variety of 1. Introduction morphological features that can be classified into three different types: broad fans, narrow jets and The optical, spectrocopic and infrared remote complex plumes. In this work, we investigate the imaging system (OSIRIS) scientific imaging cameras morphology of these events and characterize their on the Rosetta spacecraft have been monitoring the physical properties in detail, including the surface coma activity of comet 67P/Churyumov– brightness profiles, ejected mass and speed if there Gerasimenko (67P hereafter) since their orbital are two or more sequential images acquired by the rendezvous in 2014 August. The solar heating of the same filter in short duration during the time frame of sunlit side of the nucleus surface leads to sublimation the outburst [1]. of the volatiles and to the formation of dust jets. On 2015 March 12, a small outburst was first detected 2. Methods from a part of the Imhotep region on the night side. Such mini-outbursts or night-side activities have The software, shapeviewer, provided by Vincent been observed before at comet 9P/Tempel 1 by the (2016) is used to find the source regions of the Deep Impact mission and comet 103P/Hartley 2 by detected outbursts. Notice that some of the outburst the EPOXI mission. Shortly before the close plumes emerged behind the nucleus can not be found approach to comet 9P/Tempel 1, the high-resolution their source regions. In total, we therefore found camera on the Deep Impact spacecraft found a about thousand events but only 65% has its related number of small, well-defined jets whose bases were source regions. rooted at the nucleus surface. Some of these, called limb jets, appeared to come from the darker regions 3. Results and appeared to be associated with the ice patches. A later mission of the Stardust–New Exploration of 3.1 The statistical analysis of the outbursts comet Tempel 1 (NExT) imaging of 9P/Tempel 1 Using the definition of the morphology classification allowed us to connect the jets with cliffs. Comet [2], we found almost the same ratio in type A, B and 103P/Hartley 2 also displayed several narrow jet C and two of them are changing their type (i.e. from features emitting from the un-illuminated regions A to B) during the outburst. Most of the detected beyond the terminator at the time of the flyby outbursts (71.1%) appeared in the early morning and observations. Unlike the less certain identification of 28.9% occurred after the local noon. The frequency the source regions on Tempel 1, the source region of of the outburst (Figure 1) in inbound orbit (from July the nightside jets of 103P/Hartley 2 could be clearly 10 to Aug. 12) is about twice more than that in traced to some rough surface topography. However, outbound orbit (from Aug. 12 to Sept. 5). cent. When comet 67P moved closer to its perihelion in 2015 August, the excess brightness from the coma jet activities increased to 10–25 per cent of the uniform coma at a heliocentric distance of 1.24–1.38 au.

Acknowledgements

OSIRIS was built by a consortium led by the Max-Planck-Institute fur Sonnensystemforschung, Gottingen, Germany, in collaboration with: CISAS, University of Padova, Italy; the Laboratoire d’Astrophysique de Marseille, France; the Instituto de Astrofisica Figure 1 The timeline analysis in the inbound (black- de Andalucia, CSIC, Granada, Spain; the Scientific Support Office square) and outbound (red-circle) orbits. of the European Space Agency, Noordwijk, the Netherlands; the Instituto Nacional de Tecnica Aeroespacial, Madrid, Spain; the Although some outbursts from comet 67P were Universidad Politechnica de Madrid, Spain; the Department of detected only by a single image, we can estimate how Physics and Astronomy of Uppsala University, Sweden; and the long the outbursts have last. The mean duration for Institut fur Datentechnik und Kommunikationsnetze der the detected outbursts from July 2015 to September Technischen Universitat Braunschweig, Germany. The support of 2016 is about 15 minutes. The longest event was the national funding agencies of Germany (Deutschen Zentrums found on the October 31, 2015 and it was lasting 3 fur Luft-und Raumfahrt), France (Centre National d’Etudes hours more. Spatales), Italy (Agenzia Spaziale Italiana), Spain (Ministerio de Educacion, Cultura y Deporte), Sweden (Swedish National Space Board; grant no. 74/10:2) and the ESA Technical Directorate is gratefully acknowledged. This work was also supported by grant number MOST 105-2112-M-008-002-MY3 from the Ministry of Science and Technology of Taiwan. We are indebted to the whole Rosetta mission team, Science Ground Segment, and Rosetta Mission Operation Control for their hard work in making this mission possible. References

[1] Zhong-Yi Lin, J. Knollenberg J.-B. Vincent, M. F. A’Hearn, W.-H. Ip, et al. MNRAS, Vol 469. Issue Suppl_2, S731-S740, 2017

[2] Vincent J.-B. et al. MNRAS, 462, S184, 2016

Figure 2 The duration analysis during the entire [3] Lin, Z.-Y. et al. A&A, 583, A11, 2015 mission (from July 2015 to September 2016).

3.2 The excess brightness for outburst plumes A ring masking technique is used to calculate the excess brightness of the outbursts. The calculated excess brightness from these outburst plumes ranges from a few percent to 28%. According to Lin et al. (2015) [3], the excess brightness from the coma jet activities in 2014 when comet 67P was at the heliocentric distance of 3.53–3.29 au was 3–10 per